(615a) High-Throughput Production of Graphene Nanostructures (nanoribbons and quantum dots) with Controlled Dimensions and Smooth Edge Terminations

Graphene nanostructures (GNSs): narrow strips (nanoribbons: GNRs) or nano sheets  (quantum dots: GQDs) of graphene with dimensions less than 100 nm, have attracted attention of experimentalists and theorists alike owing to their exceptional properties which include widely tunable bandgap and relativistic quantum particle nature of charge carriers leading to potential application in electronics, optics, spintronics and quantum computation. Even though numerous theoretical studies have been carried out for characterizing the GNSs, experimental studies have lagged behind. The current strategies of fabrication of GNSs, via the top-down lithographic, sonochemical and chemical techniques or via the bottom up chemical condensation and high temperature sublimation based synthesis are plagued by either low throughput or they produce GNSs with limited control on sizes and / or edge crystallographies. The sensitive dependence of the intrinsic electronic and optical properties of the GNSs on their spatial dimensions and the edge crystallography mandates a high throughput production strategy with a high degree of control on the size and the edge crystallography for most practical applications. In this talk we would demonstrate a novel nanotome (ultra-microtome) based fabrication of GNSs with controlled spatial dimensions and smooth lattice terminations from the diamond knife-based cleavage of HOPG blocks. With an overall efficiency of ~ 80 %, we achieved production of ~ 10⁸ GNRs / hour / HOPG / nanotome (and ~ 10⁵ GQDs / hour / HOPG / nanotome) which equals to or surpasses most current GNR (or GQD) production strategies. The average Raman I_D/G ratios for our GNSs (for ~ 15 nm wide GNRs ≈ 0.25 – 0.28; for ~ 30 X 30 nm GQDs ≈ 2) are one of the lowest reported till date for similar structures indicating smoother edge terminations. We will present a detailed structural, chemical, electrical and optical characterization of the as-produced GNSs.

Further we will demonstrate the following:

(1) the employment of our narrow, pristine GNRs for fabricating flexible, semiconducting thin-films with the highest mobilities reported till date (~ 20 cm²/VS) and high bandgaps (~ 35 meV for ~ 15 nm wide GNR-based thin-film);

(2) the facile tunability of the optical properties (optical bandgaps and photoluminescence emission spectra) of the GQDs via dimension / shape control.